Method of and means for producing plastic bags having separable plastic fasteners

ABSTRACT

Method of and apparatus for producing plastic bags having separable plastic fasteners. A strip of bag making material is advanced step-by-step by bag width sections into a tear sealing station where the strip is retained for a dwell interval. In the station, the separable fastener means of the bag material is subjected to ultrasonic tear sealing as by means of a sonotrode along a bag edge defining line extending across the strip. Also in such station, the thinner bag body material is heat tear sealed along the bag side edge defining line as by means of a heat bar coordinated in operation with the ultrasonic sealing. The sonotrode has a profile comprising a tear line edge and material controlling and sealing rib means spaced from the tear line sealing edge.

This invention relates to the production of plastic bags havingseparable plastic fasteners, and is more particularly concerned withimprovements in tear sealing bag material into bag sections.

Material for making plastic bags with separable plastic fasteners ofeither the press-on or slide fastener type is customarily supplied incontinuous strip form and then tear sealed across the strip materialinto bag sections. Although the strip material may consist of anextrusion in which the thin bag body part and the separable fastenersare integrally extruded, another method comprises making the strip fromseparately formed thin bag body material and separable plastic fastenermeans. The separately formed body material and fastener means are thenjoined continuously and thereafter separated into separate bag sections.In joining the bag material and the separable fastener means, theseparable fastener parts are in interlocked position and then placedbetween the margins of the folded bag body plastic film with thefasteners welded to the film by heat sealing or electronic fusion.Thereafter, the bag making film fastener strip may be advanced through aplurality of tear sealing stations where the film fastener strip issealed across the bag side edge defining lines. Then individual bagsections are obtained by tearing the sections from one another along thetear seals. By way of example, Belgian Pat. No. 664523 and German laidopen application Offenlegungsschrift No. 1629218 are referred to asrelevant to the general process of joining separable closure fastenersto bag body material and then separating the same into bag sections.

The bag making film fastener strip consists of a relatively thin filmbag body material and a separable fastener means that is joinedcoextensively along a longitudinal edge of the body material which is tobecome the top or opening ends of the bags, and which fastener means hasa substantially greater unit mass. A problem is encountered due to therelative differential in the unit mass modulus, since the fastener stripmodulus is greater, i.e., thicker, than the unit mass modulus of therelatively substantially thinner bag body material or film. Theaforesaid German publication No. 1629218 has addressed this problem byeffecting individual sealing of the body material by a cross tear sealbar and separately sealing the fastener means in a timed sequence.

The prior expedients still leave much to be desired and have variousdisadvantages, drawbacks, inefficiencies and inherent shortcomings.Namely, the spatial requirements are expanded by need for a plurality ofsuccessive stations or steps for sealing the body portion of the bagmaterial and the fastener portion of the bag material. Also, there isthe difficulty in attaining proper alignment of the respective body andfastener cross seals. This difficulty arises due to numerous factorssuch as differences in tension, differences in elasticity of thematerial from place-to-place thereon or therealong, temperatureaffecting elasticity, the type of material, and the like. Some of thedifferential cross seals or spot seals will not match along the desiredseal line. When this happens, the material must be scrapped.

By the present invention, the foregoing problems are overcome, wherebynot only is working space substantially conserved, but substantially newand improved results are attained in the cross sealing of the bagmaterial.

To this end, the present invention provides a method of producingplastic bags having separable plastic fasteners on one end, and in whichthe bags are formed by severing bag sections from a continuous integralfilm fastener strip, comprising thin bag body material havingcoextensively along a longitudinal edge separable fastener means ofsubstantially greater unit mass modulus than the bag material, therebyrequiring different tear sealing techniques to effect separation of thestrip into bag sections, advancing said strip step-by-step by bag widthsections into a tear sealing station, retaining said strip for a shortdwell interval in said station as each section is advanced into saidstation, subjecting said separable fastener means in said station duringsaid dwell interval to ultrasonic tear sealing aligned with a bag edgedefining line extending across said strip, and subjecting said bag bodymaterial in said station during each said dwell to heat tear sealingalong said bag side edge defining line and coordinated with saidultrasonic sealing.

The present invention also provides an apparatus for producing plasticbags having separable plastic fasteners on one of their ends, and inwhich the bags are formed by severing bag sections from a continuousintegral bag film comprising thin bag body material having coextensivelyalong a longitudinal edge separable fastener means of substantiallygreater unit mass modulus than the bag material, thereby requiringdifferent tear sealing techniques to effect separation of the strip intobag sections, a tear sealing station and means for advancing the stripstep-by-step by bag width sections into such station wherein the stripis retained for a short dwell interval as each section is advanced intosaid station, means in said station operable during each dwell intervalfor subjecting said separable fastener means to ultrasonic tear sealingaligned with a bag side edge defining line extending across said strip,and means in said station operable during each said dwell interval forsubjecting said bag body material to heat tear sealing along said bagside edge defining line and coordinated with said ultrasonic sealing.

Other objects, features and advantages of the invention will be readilyapparent from the following description of certain representativeembodiments thereof, taken in conjunction with the accompanying drawingsalthough variations and modifications may be effected without departingfrom the spirit and scope of the novel concepts embodied in thedisclosure and in which:

FIG. 1 is a schematic side elevational view of an automatic bag makingmachine embodying the features of the present invention;

FIG. 2 is an enlarged fragmentary perspective detail view of the crosssealing station of the apparatus;

FIG. 3 is an enlarged fragmentary elevational view taken substantiallyalong the line III--III of FIG. 2;

FIG. 4 is a view similar to FIG. 3 but showing a slight modification;and

FIG. 5 is an enlarged fragmentary perspective view showing the bagmaterial and illustrating the substantial differences in unit massmodulus of the bag body material compared to the separable closureportion of the bag material.

On reference to FIG. 1, flattened thin thermoplastic synthetic filmmaterial 10 which may be in the form of an endless extruded flattenedtube or double folded half tube of the proper width for the size of bagto be produced is supplied in endless strip form from a roll 11. Thence,the plastic film bag material 10 passes to and through a set of take-updancer roller 12 of the type customarily employed where endless materialis intermittently fed through working stations. Thermoplastic syntheticseparable fastener means 13 is supplied from a stock roll 14 and guidedby a guide roller 15 toward meeting and joining the bag body material10. Such joining is effected at a joining station 17 where the separablefastener means 13 is brought into proper orientation coextensively alonga longitudinal edge of the flattened bag body material 10. Pull rollers18 intermittently advance the plastic assembly step-by-step into andthrough a sealing station 19 where stringers of the separable fastenermeans are permanently secured by any preferred heat sealing orelectronic sealing means to the one selected bag mouth forming edge ofthe bag body material. This produces a continuous integral strip S fromwhich bag body sections are adapted to be formed by tear sealing acrossthe strip S in a tear sealing station 20 in coordinated relation withthe step-by-step advance effected by the driving or advancing rollers18. Beyond the station 20 successive bag sections 21 into which thestrip S is divided by tear seals 22 are adapted to be successively tornfrom the leading end of the strip by differentially driven tear offrollers 23 and then moved by conveyor means 24 to a desired destination.

For a better understanding of a desirable form of the continuousintegral bag making strip S for which the present invention isespecially suitable, reference may be had to FIG. 5. The foldedflattened thin bag body material 10 has coextensively along thelongitudinal bag mouth edge matching opposite margins 25 to the innersides of which are secured respective stringers 27 of the separablefastener means 13 comprising complementary separable closure or fastenerprofiles generally identified at 28 and which may be of the slider orfinger pressure closure type. In this instance, the separable fastenermeans comprises a pull flange 29 on one of the fastener strips and apull flange extension 30 on the other of the fastener strips wherebyhang-up bags are adapted to be made each having a hang-up or handleopening 31, with a reinforcing bead 32 along the top edge. Such bags canbe readily opened by pulling the pull flange 29 and the handle extension30 in opposite directions to separate the interengageable resilientlyflexible fastener profiles 28. When it is desired to close the bag, thefastener profiles 28 are pressed together into interengaging closingrelation. Joining of the stringers 27 to the margins 25 is effected byseparating the margins 25 at the station 17 and orienting the stringers27 between the margins 25, whereafter the margins 25 and the stringers27 are permanently sealed together along lines 33 in the station 19. Aswill be readily observed in FIG. 5, the separable fastener means 13 hasa much greater mass modulus than the bag body material 10, so thatdifferent tear sealing techniques are desirable to effect separation ofthe strip S into bag sections 21.

According to the present invention, a substantially new and improvedmethod is provided for effecting efficient, economical, space-saving,rapid, multi-technique tear sealing of the bag making strip S along thebag edge defining seal lines 22 in the single cross tear sealing station20. For this purpose, as the bag making strip is advanced, step-by-stepby bag width sections into the station 20 and is retained for a shortdwell interval as each section is advanced into such station, means inthe station 20 comprising an ultrasonic tear sealing device 34, which isoperable during each dwell interval for subjecting the separablefastener means 13 to ultrasonic tear sealing aligned with a bag sideedge defining line extending across the strip. Coordinated with theultrasonic sealing means, means comprising a heat sealing bar 35 in thestation 20 is operable during each dwell interval for subjecting the bagbody material to heat tear sealing along the same bag side edge definingline. Both of the means 34 and 35 operate against underlying anvil means37 in this instance in the form of a freely rotatable roller 37 mountedon an axle 38 carried by fixed frame means 39. The strip S is firmlysupported on the anvil 37 for the tear sealing procedure. While the bar35 is desirably simply a heated bar which for its tear sealing functionmay be heated to about 400° C., the ultrasonic tear sealing device 34 isdesirably in the form of a sonotrode which operates at much lowerworking temperatures. The bar 35 functions by melting the plastic bagmaterial 10 by external application of heat by contacting the bag bodymaterial 10 with an elongate heat sealing edge 36 of the bar. On theother hand, the sonotrode 34 functions by means of ultrasonic impulsescausing fusion by internal molecular agitation or energization of theplastic material engaged thereby and is effective in a more limited areathan where external heat is applied to effect fusion. Therefore, thetear sealing action of the sonotrode 34 is more desirable in respect tothe greater mass modulus of the fastener means 13 than the direct heatsealing, that is suitable by means of the bar 35 with respect to themuch smaller mass modulus of the bag body material 10.

In a desirable arrangement, the sonotrode 34 and the bar 35 are mountedfor coordinated but independent movement into and out of heat and tearsealing engagement with the anvil 37. For this purpose, the sonotrode 34is mounted for vertical reciprocations toward and away from the anvil 37by means of an operating structure 40 mounted on a bracket 41 which isvertically reciprocatingly guided by a dovetail channel way 42 on amachine frame 43. A direct acting pressure fluid actuator 44 which maybe a pneumatic cylinder carried by the frame 43 has an operating piston45 secured to the bracket 41. It will be understood that operation ofthe actuator 44 for driving the sonotrode 34 into and out of heatsealing engagement with the anvil 37 is sequentially coordinated withthe sealing station 19 and the advancing means rollers 18.

For its function, the heat sealing bar 35 is mounted on a horizontalframe 47 extending in suitably spaced overlying relation to the path ofthe strip S and carried by vertically reciprocable bars 48 to which theopposite ends of the elongate frame 47 are secured. Suitable means, notshown, are provided for vertically reciprocating the bars 48 and therebythe frame 47 and the bar 35 thorugh a narrow vertical range of movementinto and out of heat and tear sealing engagement with the anvil 37 andthrough the bag body material 10, in coordination with the sonotrode 34.A clearance opening 46 in the heat bar carrying frame 47 accommodatesthe sonotrode 34 operatively therethrough in depending relation.

It is desirable to have the sonotrode 34 and the bar 35 separatelyactivated because in each tear sealing cycle, it is desirable to advancethe sonotrode 34 into its heat and tear sealing engagement with thefastener means 13 sufficiently, but only slightly, in advance of theengagement of the heat sealing bar edge 37 with the bag body material10. In practice, however, the entire tear sealing operation may takeonly about 1/10 of a second.

In order to prevent overheating the sonotrode 34 by the heat from theadjacent end of the heat sealing bar 35, a heat shield 49 is carried bythe frame 47 and depends into a gap between the adjacent ends of thesonotrode 34 and the bar 35. In addition, the sonotrode 34 is desirablyair cooled by means of a nozzle 50 directed theretoward and suppliedwith cooling air as by means of a duct 51 connected to the nozzle. Itmay be desirable to operate the air nozzle 50 intermittently incoordination with the operation of the sonotrode in its tear sealingfunction so as to also effect cooling of the tear seal formed by thesonotrode 34 at the end of each tear seal forming stroke of thesonotrode and continuing until the strip S has been advanced another bagsection through the station 20 and the sonotrode is again cycled into atear sealing stroke.

As best visualized in FIG. 3, the sonotrode 34 is desirably providedwith a tear seal forming tip of special profile construction. At itstear seal forming tip, the sonotrode has a tear line profile areacomprising a primary seal forming profile 52 of a sufficient length topress a tear line at an elongate edge 53 into the fastener means 13 andtoward the anvil 37. In a preferred construction, the sides of theprimary seal forming profile 52 are at an angle of about 120° andconverge toward the edge 53 from respective parallel spaced sealingimpression profile ribs 54 which form that part of the sonotrode tipprofile along each side of the tear line forming convergently taperedprimary profile area 52. Each of the ribs 54 projects from the tip ofthe sonotrode 34 less than the tear line forming profile area 52, butnevertheless sufficiently so that each of the ribs 54 presses sealinglypartially into the softened thermoplastic fastener means 13. Inaddition, the ribs serve as retainers against undesirable squeezingdisplacement to opposite sides of the tear line forming structure of theplastic materials i.e., incident to the forming action of the profilearea 52 thereby providing a better watertight seal at this location.Each of the ribs 54 may be of a stepped cross-sectional shape as shownwhereby the parallel sealing lines formed thereby in the fastener means13 will be of a complementary stepped cross-sectional indented profileformation.

If preferred, the sonotrode 34 may have a forming tip profilearrangement as shown in FIG. 4, wherein the tear line forming profilearea 52 may be substantially the same as in FIG. 3, but the profile ribs54' may be narrower and shallower than the corresponding ribs 54 in FIG.3. Nevertheless, the ribs 54' serve a similar function and assurethorough sealing of the fastener means 13 along the tear seal andretention of the material against undesirable spreading lateraldisplacement away from the tear line defined by the profile area 52 andmore particularly the tear line edge 53 thereof.

By having the edge 53 of the sonotrode 34 and the edge 36 of the bar 35in longitudinal alignment, the tear seal along each edge of each of thebag sections is rapidly and efficiently effected by the coordinatedoperation of the sonotrode 34 and the heat sealing bar 35 in minimumspace and with assured accuracy and efficiency and free from distortionswhich have been experienced where heat sealing has been effected inseparate spaced steps.

It will be understood that variations and modifications may be effectedwithout departing from the spirit and scope of the novel concepts ofthis invention.

I claim as my invention:
 1. In a method of producing plastic bags having separable plastic fasteners on one end, and in which the bags are formed by severing bag sections from a continuous integral film and fastener strip in which thin bag body material has in a relatively narrow area extending coextensively along a longitudinal edge separable fastener means of substantially greater unit mass modulus than the bag body material, and the body material and the fastener means thereby requiring different tear sealing techniques to effect separation of said strip into bag sections:advancing said strip step-by-step by bag width sections into a tear sealing station; retaining said strip for a short dwell interval in said station as each section is advanced into said station; subjecting said relatively narrow separable fastener means area in said station during said dwell interval to ultrasonic tear sealing including pressing thereacross and into the fastener means area a first elongate tear sealing edge means along a bag edge defining line which extends across said strip; and subjecting said bag body material in said station during each said dwell to heat tear sealing along said bag side edge defining line including pressing a second elongate tear sealing edge means longitudinally aligned with but separated at its adjacent end from said first edge means and coordinated in operation with said ultrasonic sealing first edge means.
 2. A method according to claim 1, comprising effecting said ultrasonic tear sealing by operating a sonotrode having said first edge means.
 3. A method according to claim 2, which comprises operating said sonotrode reciprocably into and out of engagement with the fastener means in advance of operation of said second tear sealing edge means.
 4. A method according to claim 1, which comprises driving said first edge means as a tear line forming profile into and across said separable fastener means, and coordinated therewith pressing sealing and material displacement profile ribs parallel to and spaced laterally at opposite sides of said tear line profile area into said fastener means area to less depth than said first edge means.
 5. A method according to claim 1, comprising during said ultrasonic tear sealing forming a tear line across said fastener means area by the pressing of said first edge means and also effecting sealing impressions into said fastener means area to less depth than said first edge means and in parallel spaced relation at opposite sides of the tear line.
 6. A method according to claim 1, comprising by the pressing of said first edge means forming a tear seal line across said fastener means area, and controlling lateral displacement of material of the fastener means area at opposite sides of the tear line by impressing stepped profiles into said area adjacently spaced from said first edge means.
 7. A method according to claim 1, which comprises providing a heat shield between the adjacent ends of said first and second edge means.
 8. A method according to claim 1, which comprises applying temperature controlling air to said first edge means.
 9. An apparatus for producing plastic bags having separable plastic fasteners on one of their ends, and in which the bags are formed by severing bag sections from a continuous integral film and fastener strip in which thin bag body material has in a relatively narrow area extending coextensively along a longitudinal edge separable fastener means of substantially greater unit mass modulus than the bag body material, and the body material and the fastener means thereby requiring different tear sealing techniques in order to effect separation of said strip into bag sections:a tear sealing station and means for advancing said strip step-by-step by bag width sections into such station wherein said strip is retained for a short dwell interval as each section is advanced into said station including a first elongate tear sealing edge; means in said station operable during each dwell interval and adapted for subjecting said relatively narrow separable fastener means area to ultrasonic heating and tear sealing pressure by said first edge aligned with a bag side edge defining line extending across said strip; and means in said station including a second elongate tear sealing edge longitudinally aligned with but separated at its adjacent end from said first edge an operable during each said dwell interval for subjecting said bag body material to heat tear sealing along said bag side edge defining line and coordinated in operation with said ultrasonic sealing means first edge.
 10. Apparatus according to claim 9, wherein said ultrasonic tear sealing means comprises a sonotrode having said first edge.
 11. Apparatus according to claim 10, including means for operating said sonotrode reciprocably into and out of engagement with the fastener means in advance of operation of said second tear sealing edge.
 12. Apparatus according to claim 9, wherein said first tear sealing edge comprises a tear line profile, and profile ribs parallel to and spaced laterally at opposite sides of said first edge and adapted to function in coordinated relation with said first edge for pressing sealing engagement with the separable fastener means area to less depth than said first edge and for controlling material displacement relative to the action of said profile area.
 13. Apparatus according to claim 9, comprising sealing impression ribs located in parallel spaced relation at opposite sides of said first edge for pressing into and across said area to less depth and said first edge.
 14. Apparatus according to claim 9, including structure for controlling lateral displacement of material of the fastener means area to opposite sides of said tear line forming first edge.
 15. Apparatus according to claim 9, including a heat shield between the adjacent ends of said first and second edges.
 16. Apparatus according to claim 9, including means for applying temperature controlling air on said first edge means.
 17. In a method of producing plastic bags having separable plastic fasteners on one end, and in which the bags are formed by severing bag sections from a continuous integral film fastener strip in which thin bag body material has coextensively along a longitudinal edge separable fastener means of substantially greater unit mass modulus than the bag material thereby requiring different tear sealing techniques to effect separation of said strip into bag sections:advancing said strip step-by-step by bag width sections into a tear sealing station; retaining said strip for a short dwell interval in said station as each section is advanced into said station; operating a sonotrode and thereby subjecting said separable fastener means in said station during said dwell interval to ultrasonic tear sealing aligned with a bag edge defining line extending across said strip; and operating a heat bar aligned with but adjacently spaced at one end from one end of said sonotrode and thereby subjecting said bag body material in said station during each said dwell to heat tear sealing along said bag side edge defining line and coordinated with said ultrasonic sealing.
 18. A method according to claim 17, which comprises providing a heat shield between said adjacent ends of the sonotrode and the heat bar.
 19. A method according to claim 17, which comprises applying temperature controlling air to said sonotrode.
 20. An apparatus for producing plastic bags having separable plastic fasteners on one of their ends, and in which the bags are formed by severing bag sections from a continuous integral film fastener strip in which thin bag body material has coextensively along a longitudinal edge separable fastener means of substantially greater unit mass modulus than the bag material thereby requiring different tear sealing techniques in order to effect separation of said strip into bag sections:a tear sealing station and means for advancing said strip step-by-step by bag width sections into such station wherein said strip is retained for a short dwell interval as each section is advanced into said station; means comprising a sonotrode in said station operable during each dwell interval for subjecting said separable fastener means to ultrasonic tear sealing aligned with a bag side edge defining line extending across said strip; and means in said station comprising a heat bar aligned with but adjacently spaced at one end from one end of said sonotrode and operable during each said dwell interval for subjecting said bag body material to heat tear sealing along said bag side edge defining line and coordinated with said ultrasonic sealing means.
 21. Apparatus according to claim 20, including a heat shield between said adjacent ends of the sonotrode and the heat bar.
 22. Apparatus according to claim 20, including means for applying temperature controlling air on the sonotrode. 